Hi, I'm in the process of installing a heater on a 2000 Xstar with Indmar 350 engine. From looking at some other threads, the normal, location to tap in to the hot water is on top of the engine. As can be seen from the pic here, both are being used already.however. I need to tee one of these to add the hose barb or try another location.

The second pic shows an Allen headed blank that I am thinking I can use, wondering if anybody can confirm. It is on the port side just below the temp sender. Any thoughts?

in the pic on the bottom, the "square" nut right above the pully on the right side of the photo is where you should tap for the return line. No reason not to tee off of an existing hot water line (presumably you have a shower?).

I was planning on teeing into the raw water intake for the return as it apparently provides a little more heat. May try the one you suggest in the first instance. No shower , the usual pickup is down low on the block by the drain plugs.

You need a Y pipe if you are going to use the raw water intake for the return. That will help low RPM heater performance a little, but it's not miraculous compared to returning to the engine water pump.

For reference, here's where PCM says to tap for the heater (remember that indmar, PCM, and everybody else uses essentially the same long blocks):

Note that the plug in your picture is the one on the top of the pump, while PCM says use the one on the side. It's a fielder's choice, either will work.

Thanks. Both outlets on the top of the inlet manifold are being used. On the starboard side, it looks as if there are two temp senders, one on top of the manifold,,the other just below it (the opposite location to the allen headed blank I attached an image of). That's why i am wondering if I can use this blank instead of teeing the starboard side and then having to faff about ensuring the sender gets a good earth (tee will use prefer tape) .